Amido phenol esters are used as bleach activators in detergents and cleaners. They permit a bleaching action even at temperatures below 60.degree. C. by reacting with a source of hydrogen peroxide--in most cases perborates or percarbonates--to release an inorganic peroxy acid.
The patent literature describes various synthesis processes for these bleach activators.
For example, U.S. Pat. No. 5,523,434 describes the preparation of amido phenyl esters from amidocarboxylic acids and phenol sulfonates by a two-stage process: in the first step an amidocarboxylic acid chloride is synthesized by reacting the amidocarboxylic acid with inorganic acid chlorides and, in a second step, the amidocarboxylic acid chloride is reacted with a phenol sulfonate in a water/diethyl ether mixture. A problem for the large-scale applicability of this process is the use of diethyl ether as solvent. Further disadvantages are low yields and the use of large excesses of inorganic acid chloride in the synthesis of the amidocarboxylic acid dichloride.
U.S. Pat. No. 5,466,840 likewise describes a multistage synthesis process for amido phenyl ester sulfonates. In the process, the alkali metal salt of a 4-hydroxybenzenesulfonic acid is reacted with a C.sub.2 -C.sub.4 -carboxylic anhydride to give the alkali metal salt of a 4-acyloxybenzenesulfonic acid. The latter is converted, in the second step, to the amido phenyl ester sulfonate by adding 1-oxyalkanoylaminocarboxylic acid in the presence of a transesterification catalyst at from 150 to 250.degree. C. over the course of from 0.5 to 10 hours. The formation of byproducts, losses in yield and complex procedures for purifying the products raise the price of the preparation of this class of substance, used as bleach activators in detergents and cleaners.
In the process according to WO 96/39378, amidocarboxylic acid and a phenol derivative are initially introduced into sulfolane, a carboxylic anhydride, for example acetic anhydride, is added dropwise and, by heating to about 170.degree. C., the conversion to amido phenyl ester sulfonates is achieved over the course of from 0.5 to 10 hours, depending on the starting compound.
Unsatisfactory aspects are the very high energy expenditure while carrying out the reaction, reduced yields, heavily contaminated products, and the very complex and cost-intensive removal of the high-boiling solvent and a very complex recycling of waste gases, byproducts and solvents. The object was therefore to find an improved procedure for preparing amido phenyl ester sulfonates.
It has been found that the slow dropwise addition of an acid halide at from 20 to 130.degree. C. to a solvent-free melt of amidocarboxylic acid and a further reaction of the degassed intermediate amidocarboxylic acid halide with anhydrous phenol sulfonate or a phenol derivative, suspended in a polar, aprotic solvent, at from 20 to 130.degree. C. gives amido phenyl ester sulfonates in very pure form and in high yields. Advantages include a significantly lower expenditure of energy than for current processes, simple removal of the solvent by precipitation of the product, solvent-free and thus readily reusable waste gases, and a reduction in byproducts, in particular in salts.